Twenty people have been tortured then murdered in a gruesome massacre at a Pakistani Sufi shrine in Punjab

At least four others suffered injuries in the attack at the shrine, believed to have been carried out by the custodian Abdul Waheed.

The shrine, named after the late boxer Mohammed Ali, a convert to Islam, is known in the area as a popular place of pilgrimage and healing for Sufi Muslims in a remote town, Sargodha.

Deputy police commissioner Liaqat Ali Chattha said the custodian called asked people to visit. 'As they kept arriving, they were torturing and murdering them,' he told told Geo TV.

The Mirror reported that four women were among those killed and that three suspects have been arrested, including the custodian, aged 50.

It is reported that the victims were drugged, stripped and then killed with a dagger and stick.

The custodian is reported to have confessed he did it because he feared that they had come to kill him. There are also reports of mental instability.

According to the BBC, the shrine was run by a Sufi saint, Muhammad Ali Gujjar, who was not there on the day of the murders.

'The 50-year-old shrine custodian Abdul Waheed has confessed that he killed these people because he feared that they had come to kill him,' Zulfiqar Hameed told AFP.

Pervaiz Haider, a doctor in a Sargodha hospital, said most of the dead were hit on the back of the neck. 'There are bruises and wounds inflicted by a club and dagger on the bodies of victims,' he told Reuters, who tried without success to find contact details for Waheed or any lawyer representing him.

Sufi Muslims are regarded as heretics by some hardliners because of the mystical element of the tradition. A suicide bombing by Islamic State killed more than 80 worshippers at a shrine in Lal Shahbaz Qalandar shrine in southern Sindh province. Last November, more than 50 people were killed in another Islamic State attack at a Sufi shrine in south-west Pakistan.

Additional reporting by Reuters